Radiation detector with a detection field comprising scintillators and photodiodes

ABSTRACT

The invention relates to a radiation detector for detecting radiation impinging in a detection zone, having detector elements which are arranged in the form of a preferably two-dimensional array in rows and columns running orthogonally with respect to one another and each have a scintillator and a photodiode interacting with the latter. In this case, detector elements arranged at the edge of array are provided, whose scintillators have an extent transversely with respect to the edge of the array which is larger than is necessary for encompassing the detection zone.

[0001] The invention relates to a radiation detector for detecting radiation impinging in a detection zone, having detector elements which are arranged in the form of an array and each have scintillator and a photodiode interacting with the latter.

[0002] In radiation detectors of this type which are used for example in the form of so-called multi-row detectors in computer tomographs, in the interests of signal paths that are as short as possible, active semiconductor components are to be mounted as near as possible to the detector area on which the X-ray radiation impinges.

[0003] These active semiconductor components are sensitive to X-ray radiation and may be damaged or even destroyed by X-ray radiation.

[0004]FIG. 1, which shows a radiation detector provided for X-ray radiation according to the prior art, reveals that even when insertion of the pencil of X-rays emerging from the focus F is prevented by collimator plates 1, that X-ray radiation emerging from the focus F can pass directly to the semiconductor components 2, there is the risk that, in particular as a result of X-ray radiation which is indicated by dashed lines, impinges on the scintillators 3 arranged at the edge of the array and is indicated by dashed arrows in FIG. 1, scattered radiation will arise which, as is indicated by dotted arrows designated by SR, passes through the semiconductor components 2.

[0005] In order to shield the semiconductor components 2 in particular also against scattered radiation SR arising in the scintillators 3, it is possible, in the manner revealed in FIG. 2, to position material 4 that greatly absorbs X-ray radiation, e.g. lead, between a scintillator 3 situated at the edge of the array and the semiconductor component 2.

[0006] This procedure is costly and complicated since a separate individual part has to be designed, produced and incorporated. Moreover, during incorporation, the bonding wires 5 between the to the photodiodes 6 of the detector elements and the semiconductor element 2 may be damaged.

[0007] Alternatively, it is possible to mount the semiconductor components further away from the active detector area, which entails, besides the higher susceptibility to interference, a great outlay, since the lines emerging from the numerous photodiodes have to be led via cables and, if appropriate, plugged connections to the semiconductor components.

[0008] The invention is based on the object of designing a radiation detector of the type mentioned in the introduction in such a way that, in a simple and cost-effective manner, in particular without additional structural parts, the preconditions are created from being able to position active semiconductor components near to the detector area without there being an appreciable risk of the semiconductor components being damaged by the radiation to the detected.

[0009] According to the invention, this object is achieved by means of a radiation detector in accordance with patent claim 1.

[0010] The enlarged extent of the detector elements arranged at the edge of the array beyond the detection zone results in a number advantages:

[0011] the region of the scintillators on which, on account of the enlarged extent, X-ray radiation does not directly impinge, which region is designated as passive region hereinafter, absorbs the scattered radiation which propagates from that region of the scintillators of the detector elements arranged at the edge of the array on which radiation directly impinges, which region is designated as active region hereinafter, in the direction of semiconductor components arranged at the edge of the array.

[0012] in the event of displacements of the radiation source relative to the radiation detector, which occurs for example as a result of thermally governed shifts in the focus of the X-ray source in the case of CT devices, the radiation continues to fall onto the scintillator material, thereby avoiding image artifacts caused by shifts in the radiation source.

[0013] the protection of the semiconductor components against scattered radiation is achieved in a very cost-effective manner since, during the production of the radiation detector, only the detector elements arranged at the edge of the array have to be dimensioned with an enlarged extent transversely with respect to the edge of the array, the additional material costs generally being of little consequence. Additional parts and work operations are not required.

[0014] In accordance with a preferred embodiment of the invention, it is provided that the scintillators have a scintillator thickness measured in the direction of the incident radiation and the extent of the scintillators of the detector elements arranged at the edge of the array transversely with respect to the edge of the array is larger by an amount lying in the range from 0.5 to 1.2 times the scintillator thickness. Assuming that the scintillator thickness, in a generally customary manner, is dimensioned such that at least 90% of the primary radiation is absorbed, then 70% to 100% of the scattered radiation is absorbed in the passive region.

[0015] An advantageous variant of the invention provides for the photodiodes associated with the detector elements arranged at the edge of the array to have an extent transversely with respect to the edge of the array which is enlarged in accordance with the associated scintillators. In this way, firstly the scattered radiation generated in the active region, which scattered radiation, as primary radiation, has previously traversed the object under examination, e.g. a patient, is utilized for imaging and the radiation dose which has to be fed to an object under examination is thus reduced. Moreover, the visible light generated in the active region is partly scattered into the passive region and passes to that part of the photodiodes which is assigned to the passive region, so that the light quanta scattered into the passive region also contributes to the output signal of the radiation detector and are not lost; rather, the light yield rises in the detector elements arranged at the edge of the array.

[0016] The detector elements are preferably arranged in rows and columns running orthogonally with respect to one another.

[0017] In the diagrammatic drawings enclosed for elucidating the invention:

[0018]FIGS. 1 and 2 show radiation detectors according to the prior art in crossed section,

[0019]FIG. 3 shows, in an illustration analogous to FIGS. 1 and 2, a radiation detector according to the invention, and

[0020]FIG. 4 shows a plan view of the radiation detector in accordance with FIG. 3 with the viewing direction on the detector area.

[0021] As can be seen from FIG. 3 in conjunction with FIG. 4, the radiation detector according to the invention, which is provided, in the case of the exemplary embodiment described, for the detection of X-ray radiation in a CT device, for example, has a substrate 7 on which detector elements are arranged in orthogonal columns and rows in the form of a two-dimensional array. The detector elements are each formed by a scintillator 3 or 3′ and a photodiode 6 or 6′, not all of the scintillators and photodiodes being provided with a reference symbol for reasons of clarity. In a manner that is known per se and is likewise not illustrated, the detector elements are separated from one another by septa which are opaque to visible light and/or X-ray radiation.

[0022] The arrangement is implemented such that the photodiodes 6 or 6′ are formed in the form of a two-dimensional array on the substrate 7 and the scintillators 3 or 3′ are for their part fitted on the photodiodes 6 or 6′ in the form of a corresponding array by adhesive bonding, for example. In this case, the scintillators 3 face the focus F of the radiation to be detected by means of the radiation detector, X-ray radiation in the case of the exemplary embodiment described.

[0023] The photodiodes are connected by bonding wires 5 to semiconductor components 2 which are arranged on the substrate 7 along the edges of the array of detector elements. For their part, the semiconductor components 2, not all of which are provided with a reference symbol for reasons of clarity, are connected to an electronic signal acquisition unit in a manner that is not illustrated.

[0024] If X-ray radiation emerging from the focus F passes to the scintillators 3 or 3′, then it is converted into visible light in the scintillators 3 or 3′, which light is detected by the photodiode 6 or 6′ assigned to the respective scintillator 3 or 3′ and is converted into an electric current which passes via the respective bonding wire 5 to a semiconductor component 2.

[0025] Collimator plates 1, as can be seen from the marginal rays of the X-ray radiation which are designated by BR in FIG. 3, ensure that X-ray radiation emerging from the focus F can only impinge on a region of the radiation detector which is designated hereinafter as detection zone and is designated by DF in FIGS. 3 and 4.

[0026] Both the scintillators 3′ and the photodiodes 6′ of the detector elements arranged at the edge of the array have an extent b′ transversely with respect to the edge of the array which is larger than is intrinsically necessary for encompassing the detection zone DF.

[0027] If the extent of the scintillators 3′ situated at the edge of the array which suffices for encompassing the detection DF is equal to b, then the following holds true for the extent b′ of the scintillators 3′ situated at the edge of the array

b+0,5*d≦b′≦b+1,2*d

[0028] where d is the scintillator thickness measured in the direction of the incident X-ray radiation, this thickness being depicted in FIG. 3.

[0029] In addition to the active region which is required for detecting the X-ray radiation impinging in the detection zone DF and is designated by a in FIGS. 3 and 4, the detector elements situated at the edge of the array thus also have a passive region, designated by p in FIGS. 3 and 4.

[0030] In this case, although X-ray radiation does not directly impinge on the passive region p of the detector element on account of the enlarged extent, the passive region nonetheless absorbs the scattered radiation which propagates from the active region of the detector elements on which radiation directly impinges, in particular the corresponding region of the scintillators 3′ in the direction of semiconductor components 2 arranged at the edge of the array. This is illustrated in FIG. 3 by X-rays R impinging on the scintillators 3′ and corresponding rays of the scattered radiation SR which do not leave the passive region of the scintillators 3′.

[0031] Even in the event of inherently undesired shifts in the radiation source relative to the radiation detector, which occurs for example as a result of thermally governed shifts in the focus of the X-ray source in the case of CT devices, the radiation continues to fall onto the scintillator material, thereby avoiding image artifacts caused by shifts in the radiation source.

[0032] If the extent of the scintillators 3′ is chosen according to the above dimensioning rule, assuming that the scintillator thickness d is chosen such that at least 90% of the primary X-ray radiation emerging from the focus F is absorbed, then 70% to 100% of the scattered radiation is absorbed in the passive region p.

[0033] Since the photodiodes 6′ associated with the scintillators 3′ have an extent transversely with respect to the edge of the array which is enlarged in accordance with the associated scintillators, firstly the scattered radiation generated in the active region a, which scattered radiation, previously as primary radiation, has traversed the object under examination, e.g. a patient, is utilized e.g. for imaging. Moreover, the visible light generated in an active region a is partly scattered into the corresponding passive region p and passes to that part of the photodiode 6′ which is assigned to the passive region p, so that the light quanta scattered into the passive region p also contributes to the output signal of the radiation detector and are not lost.

[0034] In the case of the exemplary embodiment described, the detector elements are arranged in parallel rows and parallel columns running orthogonally with respect to one another in the form of two-dimensional array. However, the invention can also be employed in those two-dimensional arrays in which the columns do not run orthogonally with respect to the rows or the detector elements are not arranged in rows and columns.

[0035] In the case of the exemplary embodiment described, the detector elements, apart from those detector elements that are arranged at the edge of the array, each have the same form and size. However, within the scope of the invention, the detector elements not situated at the edge of the array can also differ from one another with regard to their form and/or their size. In particular, these detector elements need not necessarily have the square form that can be seen from FIG. 4.

[0036] The detector elements of the radiation detector in accordance with the exemplary embodiment described above are arranged in one plane. This need not necessarily be the case within the scope of the invention. Rather, the detector elements may be arranged in a concave-cylindrically curved area, for example, as may be advantageous for the application in a CT device.

[0037] The radiation detector in accordance with the above exemplary embodiment is provided for the detection of X-ray radiation. However, it is suitable for the detection of any desired types of radiation which can be detected with the aid of detector elements composed of a scintillator and a photodiodes. 

1. A radiation detector for detecting radiation impinging in a detection zone, having detector elements which are arranged in the form of an array and each have a scintillator and a photodiode interacting with the later, which has detector elements which are arranged at the edge of the array and whose scintillators have an extent transversely with respect to the edge of the array which is larger than is necessary for encompassing the detection zone.
 2. The radiation detector as claimed in claim 1, in which the scintillators have a scintillator thickness measured in the direction of the incident radiation and the extent of the scintillators of the detector elements arranged at the edge of the array transversely with respect to the edge of the array is larger by an amount lying in the range from 0.5 to 1.2 times the scintillator thickness.
 3. The radiation detector as claimed in claim 1 or 2, whose photodiodes associated with the detector elements arranged at the edge of the array have an extent transversely with respect to the edge of the array which is enlarged in accordance with the associated scintillators.
 4. The radiation detector as claimed in claims 1 to 3, whose detector elements are arranged in the form of an array of two-dimensional arrays.
 5. The radiation detector as claimed in one of claim 4, whose detector elements are arranged in rows and columns running orthogonally with respect to one another. 